An Original Investigation into the Transcriptional Regulation of Striga Resistance in Sorghum Under Field Conditions in North Nigeria

Striga hermonthica causes catastrophic yield losses in sorghum across northern Nigeria, and while genetic resistance has been identified in some genotypes, the transcriptional regulation underlying resistance expression under field conditions in the challenging Sahel savanna environment has not been characterised, limiting the precision of molecular breeding approaches. This study conducted an original investigation into the transcriptional regulation of Striga resistance in sorghum under field conditions at Maiduguri (Borno) and Kano research farms. A field-based transcriptomics methodology was employed, using resistant (SDS-1) and susceptible (Kaura) sorghum lines grown in Striga-infested and non-infested field plots. Root tissue samples were collected at 21, 35, and 49 days after sorghum sowing (covering the underground parasite attachment window) for RNA extraction and Illumina strand-specific RNA-Seq. Differentially expressed gene analysis, weighted gene co-expression network analysis (WGCNA), and cis-element analysis of co-expressed gene promoters were performed. WGCNA identified 14 co-expression modules, of which three showed significant correlation with Striga resistance phenotype. Key transcriptional regulators in resistant modules included NAC domain proteins, ERF transcription factors, and a novel bHLH factor (SbSTR1) showing 47-fold higher expression in resistant lines at Striga attachment sites. cis-element analysis confirmed W-box elements (WRKY binding sites) in 68 percent of SbSTR1 co-expressed gene promoters, suggesting WRKY-mediated regulation. The study makes original contributions to Striga resistance transcriptomics and identifies SbSTR1 as a priority functional characterisation target for marker-assisted breeding.

Keywords: Striga resistance, sorghum transcriptomics, WGCNA, transcriptional regulation, Nigeria